The invention relates to an arrangement for cancelling spurious signals inherent to a multiplexed video signal occurring at an output of a detector formed by a linear array of elements arranged along the same line and effecting scanning of the scene, said signal first being amplified and thereafter converted into the digital form for processing the picture and finally being reconverted into the analog form.
This arrangement is, for example, used in new-generation infrared detectors.
These detectors are constituted by IR sensors which are coupled to charge transfer devices or similar devices. Thus, the function of converting the incident flux into an electric signal and also the function of integrating currents and multiplexing them so as to form a serial video signal are realized at the outputs of these detectors.
The first generation detectors only performed the flux conversion function. Cancelling the spurious signals coming from these detectors is simply effected by adding a filtering capacitor to each detector element in the region of the preamplifier. The signal multiplexing operation is thereafter effected by means of appropriate circuits.
In the new-generation detectors one has no access to the basic information of each detector. The flux conversion and multiplexing functions are not separate functions. Consequently the signal at the output of the detector is no longer available in the same manner.
The useful signals obtained from scanning the scene in polar or rectanguluar coordinates now appear serially at the output of the detector and are modulated in a given frequency range. A spurious direct current, low-frequency frequency signal is superimposed on these useful signals and has to be cancelled, the spurious signal being the result of the response of the detector to the average temperature of the background or to the temperature of the arrangement of the objective, to electric offsets between the different channels and to the low-frequency noise of the integrating and multiplexing arrangement.